FLUORESCENT CHEMOSENSOR FOR ORGANIC GUESTS AND COPPER(II) ION BASED ON DANSYLDIETHYLENETRIAMINE-MODIFIED BETA-CYCLODEXTRIN

A modified cyclodextrin containing a dansyldiethylenetriamine metal-bi nding group N(N''-dansyldiethylenetriamino)-beta-cyclodextrin, CD-dien -DNS) was synthesized. The conformation of CD-dien-DNS was studied by 2D NMR (ROESY spectral in D2O, by circular dichroism, and by fluoresce nce. The results were compared with those previously obtained with the analogous y-6-N-(N'-dansylethylenediamino)-beta-cyclodextrin (CD-en-D NS) and were consistent with the self-inclusion of the dansyl group wi thin the macrocycle cavity. However, the orientation of the dansyl gro up for CD-dien-DNS was found to be equatorial, whereas for CD-en-DNS i t was axial, suggesting a dependence of the orientation of the dansyl group upon the length of the linker. In the presence of lipophilic org anic molecules, CD-dien-DNS showed sensing properties similar to those observed for CD-en-DNS, suggesting a similar ''in-out'' movement of t he dansyl group, due to competitive inclusion of the guest. Unlike CD- en-DNS, CD-dien-DNS was found to be a fluorescent chemosensor for copp er(II) ion, with a linear response up to a 1:1 molar ratio, suggesting that a more flexible conformation of the linker and the presence of a dditional binding sites allow binding of the metal ion by the amino an d sulfonamidate groups. Good selectivity for Cu(II), when compared wit h Fe(II), Co(II), Ni(II), and Zn(II), was observed. The CD-dien-DNS co pper(II) complex was shown to behave as a chemosensor for bifunctional molecules, such as amino acids. In fact, upon addition of alanine, tr yptophan, and thyroxine, the negligible fluorescence intensity of Cu(C D-dien-DNS) complex was ''switched on'', with a response dependent on the amino acid side chain.